In recent years, a higher wiring density has been demanded for a wiring plate with the advancement of functionality of electronic devices. As a wiring plate at such a high wiring density, there are known a multilayer wiring plate (hereinafter, sometimes called “multiwire wiring plate”) which includes a circuit formed by wiring an insulation-coated wire (hereinafter, sometimes called “insulation coated wire”. A “wire” means a core wire to be a signal line, and is sometimes called “signal line”.) and a multilayer wiring plate (hereinafter, sometimes called “general multilayer wiring plate”) which does not include a circuit by the insulation coated wire, and for which a circuit is formed by circuit-processing a metal film formed of copper foil or a plated layer. Hereinafter, the multiwire wiring plate or the general multilayer wiring plate is sometimes, simply called “multilayer wiring plate”.
One example of the multiwire wiring plate is, as disclosed in Japanese Examined Patent Publication No. S45-021434 (Patent Literature 1), the one fabricated by forming an adhesive sheet for wiring (an insulating layer having adhesiveness to an insulation coated wire) on an inner layer circuit board where circuits of a power source, a ground and the like are formed, then wiring a wire insulation-coated with a polyimide resin or the like by a numerical control wiring machine, fixing the insulation coated wire by lamination by heating and pressurizing or the like, opening a penetration hole that passes through a wire (signal line) of the insulation coated wire, executing plating inside the penetration hole, and forming a through-hole connecting the formed plated layer to the wire. Here, wiring is an operation of routing the insulation coated wire on the adhesive sheet for wiring and simultaneously bonding the insulation coated wire to the adhesive sheet by ultrasonic waves.
One example of the general multilayer wiring plate is the one fabricated by laminating a plurality of inner layer circuit boards each having an inner layer circuit, opening a penetration hole so as to pass through the inner layer circuits, executing plating to the whole including the penetration hole, forming a through-hole connecting the formed plated layer to the inner layer circuits, and executing circuit-processing to the copper foil of an outermost layer and the plated layer. As a method of the circuit-processing, there are generally known a forming method of etching and removing an unrequired part of the copper foil or the plated layer (subtraction method), a forming method of plating a required part (additive method), and a forming method of plating the required part of the copper foil or the plated layer and then etching and removing the unrequired part of the copper foil or the plated layer (semi-additive method). Hereinafter, the circuit formed by etching and removing the unrequired part of the copper foil (metal foil) or the plated layer is sometimes called “etching circuit”. As in the subtraction method, the additive method and the semi-additive method described above, the circuit formed by circuit-processing the metal film formed by the copper foil (metal foil) or the plated layer is sometimes called “metal film circuit”. Moreover, as a method of laminating the plurality of inner layer circuit boards, there are known a pin lamination method of alternately piling up the plurality of inner layer circuit boards each having the inner layer circuit and insulators to be insulating layers with a positioning pin as a reference, and laminating them altogether by heating and pressurizing, and a buildup method of forming a desired number of wiring layers by repeating, for a required number of times, a process of piling up and laminating an insulator to be an insulating layer and a copper foil layer by layer on an inner layer circuit board having an inner layer circuit, forming a penetration hole or a non-penetration hole, executing plating, and forming a circuit by etching and removing the unrequired part of the copper foil and the plated layer.
On the other hand, a multilayer wiring plate that copes with a high frequency has been demanded, and as such a multilayer wiring plate, a multiwire wiring plate having a coaxial wire is known. The coaxial wire is a wire for which an outer peripheral conductor for shielding (hereinafter, sometimes called “shield layer”) is formed on an outer periphery of a wire to be a signal line through an insulating layer. As a method for fabricating the multiwire wiring plate using the coaxial wire, there is known a fabricating method of removing the insulating layer by irradiating a part where a penetration hole connecting a circuit and the wire (signal line) of the coaxial wire is formed and a part where a non-penetration hole connecting the circuit and the outer peripheral conductor (shield layer) of the coaxial wire is formed with plasma from a surface layer side of the multiwire wiring plate (Patent Literature 2).